Electric furnace for melting of high melting point metals or alloys



' Feb. 19, 1957 J. PRESTON 2,782, 45

* v ELECTRIC FURNACE FOR MELTING OF HIGH MELTING POINT METALS OR ALLOYSFiled March 25, 1955 2 Sheets-Sheet 1 i/ g: l6

INVENTOR FIG. JACK PRESTON 7 v f B W Feb. 19, 1957 J. PRESTON ELECTRICFURNACE FOR MELTING OF HIGH MELTING POINT METALS OR ALLOYS 2Sheets-Sheet 2 Filed March 25, 1955 N R0 OT TS NE E R VP W K C A J l16%, TORNEYS ELECTRIC FURNACE FOR MELTIN G OF HIGH MELTING POINT METALS RALLOYS Jack Preston, Hall Green, Birmingham, England, assignor toImperial Chemical Industries Limited, London, England, a corporation ofGreat Britain Application March 25, 1955, Serial No. 496,716

Claims priority, application Great Britain April 2, 1954 Claims. (Cl.13--9) This invention relates to an improved apparatus for use in thearc-melting of high melting point reactive metals and alloys, such forexample as titanium, zirconium, molybdenum, thorium, hafnium, tantalum,chromium and their alloys, and more particularly to'apparatus forcarrying out a process according to our copending application No.475,277.

In the specification accompanying the said application we have describeda method of arc-melting metals and alloys of the kind described byforming a coherent but incompletely melted mass of metal or alloy byfeeding the raw material to the melting chamber of an arc-meltingfurnace at a higher rate than that consistent with complete melting ofthe raw material over the whole cross section of the melting chamber,and then employing the so-obtained mass as a consumable electrode to beprogressively melted in a second arc-melting furnace having a meltingchamber of greater cross section than that of the said electrode, withor without an additional feed of raw material into the melting chamber.

According to the present invention, we provide an ap paratus forcarrying out the said process which comprises one or more cooledarc-melting crucibles superimposed above a cooled arc-melting crucibleof larger cross sectional area and in communication therewith, alongitudinally adjustable cooled base member adapted to serve as a baseclosure for either the upper or the lower crucibles, means for supplyingraw material to the crucible assembly, means for evacuating the saidassembly and if desired supplying an inert atmosphere thereto, and alongitudinally adjustable consumable electrode assembly for the uppercrucible or crucibles which is adapted to function as electrode stem inthe operation of the lower crucible.

The invention is illustrated but not limited by the accompanyingdrawings in which:

Figure 1 represents a longitudinal section through a combination furnaceat the first stage of the process, i. e. the formation of the coherentconsumable electrode; the metal to be melted being for the sake ofexample titanium.

Figure 2 is a similar section but at the second stage of the process, i.e. the commencement of the final melting stage.

Referring to the drawings, the apparatus consists essentially of awater-cooled crucible 1 in conjunction with a second water-cooledcrucible 2 of larger cross section, both crucibles being served by acommon water-cooled base plate 3.

The top of the furnace is formed by the water-cooled cone 4 carrying inits lid 5 the hopper connection 6, through which raw material insuitable form is fed from the hopper 7 to the furnace at a predeterminedrate by means of a vibrator mechanism 8, a vacuum and inert gasconnection 9, through which the furnace is evacuated by means of avacuum pump 10, and then, if desired, filled with an inert atmospheresuch as, for example, argon, and a gas seal 11 through which passes thetitanited States Patent 0 nium electrode 12. The latter may consist ofsolid titanium, for example, forged bar, or may consist of a number ofunits consolidated from the divided metal and welded or otherwise joinedtogether into a suitable length. Controlled vertical movement of theelectrode 12 is effected by means of the feed rolls l3, and theelectrode is connected to one terminal of the electrical supply by meansof suitable contact gear 14. The cone 4 and the crucibles 1 and 2 areelectrically insulated from one another by insulating rings 15 and 16.

The crucible 2 is provided with a separable flanged base member 17having a central aperture with an inclined face conforming to the base 3and adapted to act as a seating therefor, and the crucible is closed bymeans of the box 18. The base 3 is of hollow construction and issupported by the hollow stem 19 passing down through the box 18 andgas-tight seal 29. The base has an internal bafile and coolant issupplied to and from it via the stem 19. Longitudinal movement of thebase 3 is effected by any suitable mechanical means such as a rack andpinion 21. The stem is connected to the other terminal of the electricalsupply by a contact 22. The stem also carries a circular flexible brush.3 for the purpose hereinafter explained.

in operation, the hopper, cone and crucibles are first evacuated andthen refilled with an inert gas such as argon or helium. The base 3 isthen moved to the position shown in Figure 1, an initial charge of thedivided metal fed into crucible 1 from the hopper and an arc struckbetween the charge and the electrode After the initial charge is melted,the divided metal in the hopper is fed into the crucible at as fast arate as possible, consistent with the production of a coherent mass inthe crucible. The maximum feed rate is advantageous in that it limitsthe amount of electrode which is consumed in the operation. When themass 24 has been built up to a suitable height in the crucible, feedingfrom the hopper is stopped and a molten pool allowed to form at the topof the mass by maintaining the are for a further short period, forexample, one to three minutes. The electrical supply is then shut offand the electrode 12 immediately moved down into the pool by means ofthe feed rolls 13. The mass 24 in the crucible is thus joined to andbecomes integral with the electrode by the intimate fusing together ofthe two.

The base 3 is then lowered to the position shown in Figure 2 by means ofthe retracting mechanism 21. At this stage, a small amount of unmelteddivided metal in the base of crucible 1 may fall on to the inner conicalsurface of the copper seating member 17 and prevent an accurate seatingof the base 3 thereon. To obviate this, the brush 23 is secured to thestem 19 so that on loweriug the base, the brush passes through theseating aperture into the box 18 and clears any particles from theseating surface.

When the base 3 is in position, the coherent mass 2d now attached toelectrode 12 is moved down to the position shown in Figure 2, thismovement being facilitated if required by tapering the crucible 1. Aninitial charge of divided metal is fed into the base of crucible 2 fromthe hopper and an arc struck between this charge and the mass 24, whichis melted into the crucible 2; with or without an additional feed ofdivided metal from the hopper. When the mass 24 is completely melted,the electrical supply is cut off, the ingot allowed to solidify andremoved by lowering the box 13, seating member 17 and base 3. It isessential that crucible 2 should be somewhat larger than crucible 1 inorder that the mass may be fully clear of crucible 1 before itapproaches the base of the second crucible, thus a fed of divided metalmay fall through the first crucible into the second. The latter mustalso be greater in diameter to ensure that the feed 3 of divided metalmay fall freely between the mass 24 and the walls of crucible 2.

Whilst the invention has been described with reference to one particularapparatus, it will be appreciated that various modifications may be madein the apparatus and are included within the scope ofthe invention. Thusfor example the initial electrode may be totally enclosed together withits feed rolls and contact gear in a gastight tubular extension from thefurnace lid, or alternatively the electrode may be attached by suitablemeans to a water-cooled copper stem passing through the seal in thefurnace lid. The insulating ring between the upper and lower cruciblesmay be omitted, but it is preferably included to insure againstelectrical arcing and short-circuiting between the mass 24 and the uppercrucible during the melting of the mass in the lower crucible.

In a further modification, a plurality of separate upper crucibles, forexample three, may be used in conjunction with a single lower crucibleof'suificiently large diam eter. In this way, three electrode masses maybe built up and then consumed simultaneously in the formation of a largeingot in the lower crucible.

The apparatus in accordance with the present invention facilitates theformation of a large electrode from divided metal in accordance with theprocess of our aforementioned co-pending application with the minimumconsumption of preconsolidated electrode. -Moreover, by the employmentof a cooled base which serves for both crucibles it enables the meltingof this large electrode to be carried out in the same apparatus and withthe minimum time interval between formation and melting.

I claim:

1. Arc-melting furnace which comprises a cooled arcmelting cruciblesuperimposed above a cooled arc-melting crucible of larger crosssectional area, a cooled base member longitudinally adjustable betweenan upper position where it serves as a base closure for the uppercrucible and a lower position where it serves as a base closure for thelower crucible, means for supplying raw material to the crucibleassembly, means for evacuating the said assembly and a longitudinallyadjustable consumable electrode assembly for the upper crucible adaptedalso to function as a stern for an electrode formed in the uppercrucible for use in the operation of the lower crucible.

2. An arc-melting furnace according to claim 1. wherein said means forevacuating the said assembly is also adapted to supply an inertatmosphere thereto.

3. Furnace in accordance with claim 1, in which the longitudinallyadjustable consumable electrode for the upper crucible comprises solidmetal.

4. Furnace in accordance with claim 1, in which the longitudinallyadjustable consumable electrode for the upper crucible comprises anumber of units consolidated from divided metal and joined'together intoa suitable length.

5, Furnace in accordance with claim 1, in which the electrode for use inthe operation of the lower crucible is formed by allowing a molten poolto form at the top of the coherent mass in the upper crucible, movingthe end portion of the longitudinally adjustable consumable electrodedown into the pool, and allowing the molten metal to cool.

References Cited in the file of this patent UNITED STATES PATENTS2,541,764 Herres Feb. '13, 1951 2,640,860 Herres June 2, 1953 2,651,668Southern Sept. 8, 1953 2,686,822 Evans et al Aug. 17, 1954

